1. Field of the Invention
This invention relates to a method and means of providing an uninterrupted voltage regulated power supply for electronic equipment having a critical need; therefore, such as point of sale computers, other devices with volatile electronic memories, sequential or numerical control processes where supply voltage interruption could cause malfunction, hazard or equipment damage, and security systems where a power interruption could cause a non-alarm or a false alarm situation.
2. Description of the Prior Art
The use of standby or emergency power sources to protect critical loads has been a common practice for many years. Telephone companies have traditionally used 48 volt lead acid battery banks which are automatically charged from commercial power sources for PBX and central exchange operation to reduce the effect of power outages. Other areas where continuity of power supply is a critical requirement but where momentary voltage dropouts can be tolerated include airport control towers, communication centers, aircraft runway and landing lights, navigational aids, hospital operating theaters, security lights in department stores, etc. These facilities are usually equipped with gasoline engine generating sets which can assume critical loads in a matter of five to twenty-five seconds.
Engine alternator sets are usually designed to supply loads of from 5 to 150 kilowatts (or more if required). Standby or emergency generators also include load transfer relays, reliable automatic engine starters and periodic line voltage sampling facilities. Loads are not usually returned to the commercial supply until after observation of 10 to 15 minutes of uninterrupted line voltage.
Large digital computer installations generated a requirement for no-break multi-kilowatt emergency power supplies. The no-break feature can be implemented with a continuously running motor-alternator set, coupled to an inertial flywheel supply which in turn is coupled to a gasoline engine through an overrunning clutch. When the power fails, the engine starts and picks up the load through the overrunning clutch before the motor-alternator loses more than five cycles in RPM or 10 percent in line voltage. When the commercial power returns, the motor picks up the load and the engine shuts down.
The use of battery power to back up no-break supplies of 5 kw and up involves large and heavy battery installations which must be integrated into the supply chain to avoid even a momentary voltage interruption at the time of power failure.
For example, a battery back-up to maintain a 10 kw load for one hour would require 96 volts of 200 ampere hour batteries and would probably include rotating equipment, whereas the state of the art presently will allow a no-break battery back-up system of 5 kilowatts or less to operate with solid state converters.